Reconstitution of respiratory-chain enzyme systems. XVI. The effect of alkali on the succinate oxidase system

Abstract

1. The succinate dehydrogenase protein, as measured by the acid non-extractable flavin, was found to be dissociated from the particulate succinate oxidase (the heart-muscle preparation) by alkali treatment in the absence of succinate and presence of oxygen. The dissociation occurred at the same rate as the inactivation of the succinate oxidase. From the kinetic and the equilibrium results reported in this paper, it was concluded that the original site for binding of the dehydrogenase to the particle was available to link active succinate dehydrogenase during reconstitution of the succinate oxidase system. 2. The inactivation of succinate oxidase during the alkali treatment, in the absence of succinate or any reducing agent, was found to be linear with time. The rate of inactivation varied as the first power of the initial enzyme concentration and the second power of the hydroxyl ion concentration. The temperature dependence of the rate constant, however, was complex. 3. The equilibrium dissociation of the particulate succinate oxidase by alkali in the presence of succinate and absence of oxygen was examined using the acid non-extractable flavin as a measure of succinate dehydrogenase. The per cent of the dehydrogenase dissociated is a linear function of the hydroxyl ion concentration. The equilibrium constant for the dissociation is decreased by increasing the ionic strength and the Van 't Hoff isochore is not linear but exhibits positive curvature. The equilibrium constant for the dissociation determined by the acid non-extractable flavin is practically the same as that estimated by reconstitutive activity.